How to Wind a Bump Head | String Trimmer Line Guide

A bump head is usually wound by removing its spool, feeding the correct trimmer line through the spool, and winding the line in the direction shown by the arrow. Turn off and unplug the trimmer—or remove the battery—before working on the head. The exact removal method and line size vary by model, so check the owner’s manual if the head does not match these steps.

What you need

• The correct diameter of trimmer line for your head
• A length of replacement line
• Gloves and eye protection
• The trimmer’s owner’s manual, if available

Do not guess the line diameter. Line that is too thick can overload the motor or fail to feed, while line that is too thin may wear out quickly. The manual, spool, or trimmer head may list the approved size.

Steps for winding a bump head

1. Make the trimmer safe

Turn the engine off and let a gas trimmer cool. Disconnect the spark-plug wire if the manufacturer recommends it for maintenance. For a corded model, unplug it. For a cordless model, remove the battery.

Place the trimmer on a stable surface with the cutting head facing up. Wear gloves because the line cutter and worn line ends can be sharp.

2. Remove the bump-head spool

Hold the outer head still and remove the bump knob or cover according to the manufacturer’s instructions. Some heads use a threaded bump knob, while others use side tabs or a retaining cap.

Lift out the spool and note how the existing line is routed. Taking a quick photo before removing the old line can help you reproduce the correct path.

3. Prepare the replacement line

Cut the line to the length specified for the spool. Many spools use one continuous piece of line, but some heads use two separate pieces. Follow the instructions for your specific spool rather than assuming one method fits all heads.

Straighten the line before loading it. A badly kinked section can create a tight spot that prevents the line from feeding properly.

4. Find the winding direction

Look for an arrow molded into the spool. Wind the line in the direction of that arrow. Winding in the wrong direction can make the bump-feed mechanism release line incorrectly or prevent the spool from fitting back into the head.

If the arrow is worn away, consult the manual. Do not rely only on the direction the old line appears to have been wound, since it may have been installed incorrectly.

5. Anchor and wind the line

Insert the line into the spool’s anchor hole, slot, or channel. Leave the amount of line specified by the manufacturer outside the anchor point, then begin winding in the arrow’s direction.

Keep each wrap next to the previous wrap. Wind with firm, even tension, but do not pull so tightly that the line stretches or cuts into the lower layers. Crossed or loose loops can jam when the bump head rotates.

If the spool has two channels, load each side as directed. Keep the line separated and avoid overfilling either channel.

6. Secure the line in the retaining slots

When the spool is full, place the loose ends into the spool’s retaining notches or slots. This keeps the line from unwinding while you reinstall the spool.

Leave the correct amount of line extending from each side. Ends that are too long may strike the guard’s line cutter, while ends that are too short may pull back into the head.

7. Reinstall the spool and cover

Place the spool into the head with the line ends aligned with the outlet eyelets. Thread the ends through the eyelets, then reinstall the cover or bump knob.

Tighten the retaining part by hand as directed. It should be secure, but forcing a plastic cap or knob can damage the threads. Rotate the spool by hand to confirm that it turns without binding.

8. Check the feed before trimming

With the trimmer still powered off, pull each line end gently to confirm that the line can move through the eyelets. If the head uses bump feed, tap the bump knob against a firm surface only after the trimmer is running and you are in a safe, clear work area.

Keep people, pets, windows, and vehicles away from the cutting area. Use the guard supplied with the trimmer.

Common winding problems

The line will not feed

First check that the line is the approved diameter and that it was wound in the direction shown by the spool arrow. Then look for crossed wraps, an overfilled spool, or line ends trapped under the cover.

Remove the spool and rewind it neatly if necessary. A worn eyelet can also pinch the line and prevent feeding.

The line feeds too much

The spool may be overfilled, the bump knob may be worn, or the line may be too loose on the spool. Check that the head’s automatic limiter or guard-mounted cutter is present and undamaged.

Do not operate the trimmer without its guard. The guard controls the cutting length and provides protection from thrown debris.

The line keeps breaking at the head

Line can break when it is the wrong size, dried out, incorrectly wound, or repeatedly struck against concrete, edging, rocks, or other hard surfaces. Rewind the spool with fresh line and trim around hard edges carefully.

If the line breaks at the eyelet, inspect the eyelet for a sharp groove or crack. Replace the eyelet, spool, or complete head if the damaged part is not available separately.

The spool will not fit back in

Check for line wound above the spool’s retaining lip, line ends routed outside the eyelets, or a spool that was installed upside down. Remove excess line and reinstall it according to the head diagram.

Do not force the cover. A replacement spool may be needed if it is warped, cracked, or no longer matches the head.

When to replace the spool or bump head

A new line winding will usually solve a feed problem when the spool is intact and the line was simply loaded incorrectly. Replace the spool when its hub, anchor point, retaining slots, or eyelets are cracked, badly worn, or distorted.

Replace the entire bump head when the cover will not stay secured, the bump knob is damaged, the head wobbles, or replacement parts are unavailable. Use a head approved for the trimmer’s shaft and guard configuration. Disconnect the power source before removing or installing any cutting head, and follow the manufacturer’s instructions for compatibility and tightening.

If the head vibrates severely after correct installation, stop using the trimmer. A damaged head, unbalanced spool, loose fastener, or bent shaft requires correction before further operation; consult the manufacturer or a qualified repair professional when the cause is unclear.